1. Field of the Invention
The present invention relates to a digital information transferring apparatus for a Discrete Cosine Transform (DCT) compressed digital image signal, a PCM audio signal, and a control subcode, and, in particular, relates to an ID signal added to each sync block of the transferred data.
Digital VTRs are known which use, for example, rotating heads for recording digital video signals on a magnetic tape. Since digital video signals comprise a very large amount of information, digital VTRs have often employed highly efficient coding techniques for compressing the amount of recorded or transmitted data. Among these techniques, Discrete Cosine Transform (DCT) coding has been practically employed. In these digital VTRs, in addition to the DCT encoded digital video signal, a PCM audio signal and control subcode are also recorded on a magnetic tape by means of rotating heads.
In the DCT coding, one frame of image information is transformed into blocks composed of, for example, (8.times.8) picture elements or pixels, and then these blocks are processed by a cosine transform which is a kind of orthogonal transform. Thus, (8.times.8) coefficient data are generated. These coefficient data are processed with a variable length code such as, a run length code or Huffman code. Before being transferred to a receiving system, the encoded data, an ID signal, and so forth are transformed into frames so that the reproducing system can easily process the received data. Each frame may be composed of sync blocks in which a block synchronous signal is added to data at predetermined intervals. The reproducing system can then transform the frames into the desired reproduced data.
The ID signal contains a sync block number (address) and so forth. By using a cassette tape and a tape head mechanism in a digital VTR, the ID signal can be applied to an external memory (a data streamer) for use in computers. However, with the conventional ID signal, such external application has not been contemplated. In digital VTRs, the insertion of an ID signal for identifying the record mode, broadcasting system format, and so forth has been considered. However, when the digital VTR is used as an external memory for computers, an ID signal for each record mode and each broadcasting format is not necessary. Therefore, the amount of information conventionally included in the ID signal would be unnecessary and the effective data area would be undesirably reduced.